At the feeding point the root
continually abstracts water from the soil grains and thus makes the
film thinner in that locality. This causes a movement of moisture
similar to the one above described, from the wetter portions of the
soil to the portion being dried out by the action of the plant-root.
Soil many feet or even rods distant may assist in supplying such an
active root with moisture. When the thousands of tiny roots sent out
by each plant are recalled. it may well be understood what a
confusion of pulls and counter-pulls upon the soil-moisture exists
in any cultivated soil. In fact, the soil-water film may be viewed
as being in a state of trembling activity, tending to place itself
in full equilibrium with the surrounding contending forces which,
themselves, constantly change. Were it not that the water film held
closely around the soil particles is possessed of extreme mobility,
it would not be possible to meet the demands of the plants upon the
water at comparatively great distances. Even as it is, it frequently
happens that when crops are planted too thickly on dry-farms, the
soil-moisture cannot move quickly enough to the absorbing roots to
maintain plant growth, and crop failure results.
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